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Abstract

Three hundred shoots with flower buds were collected from three blueberry types to determine the influence of chilling hours on flower bud expansion. The three types were rabbiteye blueberry (Vaccinium ashei Reade) ‘Brightwell’ and clone T-110, and low-chill highbush blueberry (V. corymbosum L.) ‘Georgiagem’. Chilling hours in this study ranged from 0 to 700 and were defined as accumulated hours of temperatures < 7.2°C. Flower bud expansion of all three blueberry types was influenced significantly by levels of accumulated chilling. The mathematical relationships between bud width and chilling hours were either linear or quadratic. Largest bud expansion occurred after 400 chilling hours for ‘Brightwell’ and ‘Georgiagem’ and after 550 hr for T-110. Overall, ‘Brightwell’ had the smallest bud width, ‘Georgiagem’ was intermediate, and T-110 the largest.

The blueberry cultivar situation in North America is undergoing rapid change. Attempts to grow blueberries in non-traditional areas, and increased biotic and abiotic challenges in traditional production areas, are fueling the search for superior, adapted cultivars. This survey of all blueberry-producing states/provinces in the United States and Canada provides the current status and projected trends in blueberry cultivar use in North America. Most (86%) of current hectarage is comprised of 25 northern highbush, 10 rabbiteye, and two southern highbush cultivars. `Bluecrop' is the dominant northern highbush cultivar, with 35% of the highbush area, while `Tifblue' occupies 40% of the rabbiteye area. Some historically important cultivars, such as `Jersey', `Weymouth', and `Woodard' are in decline. New cultivars of all blueberry types are beginning to have a positive impact on the blueberry industry.

Breeding to adapt temperate-zone fruit to subtropical production areas has been a formidable objective because so many different characteristics have to be changed, most of which are controlled by many genes. Recurrent selection is the only breeding method that can accomplish the required wholesale reorganization of the physiology of the plant. The principles of recurrent selection, developed and tested using short-generation organisms like fruit flies, rats, and maize, have been applied to the development of low-chill highbush blueberry (V. corymbosum L.) and peach [Prunus persica (L.) Batsch.] cultivars for northern and central Florida. These principles include using many parents per generation of crosses, minimizing the time between cycles of selection, and selecting simultaneously for all heritable traits that are important in the final product, with traits of highest economic importance and highest heritability being given the highest weight in selecting parents. Many characteristics changed during the breeding of low-latitude peach and highbush blueberry cultivars, including chill requirement, photoperiod response, resistance to various disease and insect pests, fruit chemistry, and growth patterns during a long growing season.